UNIX for Dummies Questions & Answers

I'm watching a particular expression as it is appended in a line to a file:

Code:

tail -f LOG | sed -n /"$@"/p

So whatever value I pass into this script will tail -f the file, but only show me lines that contain the value:

Code:

lgwatch expression

However some of the output contains a #20 control character (or translation of a control character - whatever). I want it removed from the output. I tried a few variations with the scipt:

Code:

sed -n /"$@"/p;'s/\#20//g'
sed -n -e /"$@"/p;'s/\#20//g'
sed -n /"$@"/p;s/\#20//g
sed -e 's/\#20//g';/"$@"/p
sed 's/\#20//g' '/"$@"/p'

I can't seem to get these #20's removed. Can anyone suggest?

Could you show your actual output please?

Well there is no output when I add the additional sed statement - that's how I come to the conclusion that it's not working.

Obviously. I mean the output you had before, still containing the bad characters you wanted removed.

Here's an example substituting names to protect the innocent:

Code:

[user@hostname]lgwatch command
user MIKE entered command /usr/bin/tail#20-f#20/var/adm/log

I just realized something. If $@ is ever more than one parameter, it will split into individual arguments in your sed statement, even inside double-quotes! That is $@'s function, to split on arguments and nowhere else... Try "$*" inside double quotes instead.

Thanks for your continued support. I did try using an asterisk instead but I'm still not getting the desired result. I'm really confused on how to add the secondary sed statement without wrecking this whole thing. As you see before I've googled various ways to combine sed statements but it doesn't seem to be working as it should.

These attempts do not remove the #20's:

Code:

sed -n /"$*"/p | sed 's/#20//g'
sed -n /"$*"/p;'s/#20//g'
sed -n /"$*"/p | sed -e 's/#20//g'
sed -n /"$*"/p;"s/#20//g"
sed -n /"$*"/p | sed 's/\#20//g' (also with the above combinations)

I tried outputting results to a text file and then using the following sed and it worked:

Code:

sed 's/#20/ /g' txt

Granted instead I'm replacing the #20's with spaces but it still works. So I believe my sed statement is correct, but it seems I'm not appending it correctly. Can anyone advise how it should be added onto my tail command?

** Update **

I can search just for the expression I'm looking for - which gets passed into $@ or $* (tried both) so it appears that the issue is piping a sed statement for removing the #20's is the problem. Sed using -n '/$@/p' isn't a problem, but damnit if I put sed 's/#20/ /g' on the end that just kills any output. I've tried putting \#20 as well as including it in double quotes. What is the problem with my sed statement?

*** update ***

I moved the sed statement to the beginning of my tail statement and somehow this works. I guess it pulls all the #20's from everything before it does the tail...not really sure why I have to do this and piping the sed statement at the end kills it.